Help somethings wrong with my blazer

Ok here goes last time i tried explaing this i was really mad and it didnt come out right.I have a 77 blazer 350 goodwrench motor i would say about 5000 miles on it.I was on my way to work this morning and she was backfiring alittle bit it sounded like it was coming from the passenger side header right at the reducer.I come to this hill and give it gas the backfire got louder and it was kinda like it was sputtering i guess ,i had to the floor and it wouldnt go above 30 and as i kept going up the hill the speedometer kept dropping as i got to the top i noticed there was a whole lot of smoke coming in by the passenger side vent it burned the [censored] out of my eyes there still burning,anyways i pulled over at walmart and let it cool for about 15 mintues then i started it up and didnt want to start i tried a second time and got it to start i reved it up alittle bit and noticed smoke coming out of the exhaust it was it look like blackish white but i couldnt tell i made it to the light and the idle was really rough i had to litterly keep my foot on the gas and let it idle at 1000rpms.So anyways im driving home going like 20 mph the whole way here.I get to the hill at the top of my street i give it gas and its fine so now its running fine but i still really dont want to drive it i dont know what is wrong with it it only does this sometimes but this was the worse case of it.What should i do i really need my truck to go back and forth to work everyday and its really getting to be a pain not knowing if ill ever get there.Any info would greatly be appreciated

1) Your float is sticking and extra fuel is spilling out of the bowl making the mixture way too rich.

2) The ignition is cutting out somehow and not firing the mixture. You could have a couple of bad wires, a failing coil or a failing ignition module. I had an Accel HEI coil. It ate itself after about 6 months. The failure mode was a break somewhere in the winding. Sometimes the circuit would be broken and it would have to arc though, so the engine would sputter, hardly idle and have no power. Other times it would fire right.

Boy that's some weird stuff. I have to agree that I would start looking at ignition problems. Bad coil, bad modual stuff. Make Pull the top off the center of the cap and inspect the coil and the rubber insulator part under the coil. If that was bad and letting spark ark back to the coil it could cause problems like that. Another user had simular problems and found that exact problem.

Hey thanks for the info when i got home i pulled a couple plugs out there where black as can be so i put new plugs in it then i got some carb cleaner and sprayed that in the carb i dont know which one worked but its running better then it ever did before but im still gonna look at the cap and stuff this weekend.I drove it around yesterday for about a half hour and it was running really good so im going to drive it today and see what happens.

Yeah it sounds like time for some stuff like a good tuen up. New cap, plugs and possibley wires. If you have an Ohm meter you can test the plug wires.
With the plugs being plack is a concern. If it was oily then you may have a problem with Oil getting into the cylinders and fouling them out. Might be as simple as Valve guide seals. That's about $25 in parts and a afternoon of work if you have the tools to do the job if not then expect about $250.
I would do a compression test and a poor mans bleed down test ( or the real deal if you have the tools) to check the health of the engine.

Do you have two into one pipes with a catalytic convertor? If so, I had something very similar to this happen to me in a car I used to have. Took the shop two days to figure out the cat. was clogged. No power and just horrible gas mileage. The clog was so bad that exhaust gas was backing up and causing the car to misfire, soot the plugs, smoke, etc... You get the picture. Worth a shot, if you have a catalytic convertor.

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